Hot Water Storage Research Articles

Reliability and availability modelling of a retrofitted Diesel-based cogeneration system for heat and hot water demand of an isolated Antarctic base

The reduction of greenhouse gas emissions is a relevant challenge for a sustainable development. Waste heat could be used to produce hot water by using a recovery system. This article studies the availability of a combined heat and power systems (CHP) in extreme area (Antarctic) through the integration of a waste heat recovery system with a diesel generator to produce hot water. The reliability and availability principles are incorporated to explore how the profile of hot water consumption and the hot water storage tank size affect system availability. Different combined heat and power systems are thus classified, and their availability indexes modelled by adopting the continuous Markov approach and the state space model. The results indicate that the CHP systems availability is strongly influenced by the daily hot water demand profile. As a useful recommendation, one of the considerations for increasing availability, reducing costs and greenhouse gas emissions with the CHP system is to include a hot water tank in the analysis.

Experimental assessment of novel designed solar hot water storage collector incorporating an array of partitioned ducts absorber

A Novel design of a solar water collector consisting of an array of adjacent partitioned ducts representing the collector absorber is investigated experimentally. Each duct is divided into two flow passages by a partitioned plate made from insulation material. The heated water flows over the partitioned plate to the storage tank, while the cold water flows from the storage tank to the duct down the portioned plate. The designed partitioned ducts solar collector (PDSC) performance is compared to conventional flat plate solar water collectors (FPSC) with the same dimensions and materials. The study is performed under hot weather conditions of upper Egypt for collectors’ tilt angles of; 17°, 27°, and 37°. The findings reveal that PDSC has higher storage water temperature, energy storage, energy efficiency, and lower energy losses. The PDSC has average daily efficiencies of 57.5%, 55.2%, and 47.5%, with enhancement percentages of 31.2%, 32.4%, and 38.6%, relative to the FPSC, at the studied tilt angles, respectively. The PDSC has average exergy efficiencies of 4.47%, 3.71%, and 2.89%, with enhancement percentages of 36.3%, 36.5%, and 41% relative to the FPSC, at the studied tilt angles, respectively. The maximum required thermosyphon heads of the PDSC are 0.8, 0.7, and 0.1, and the corresponding values of the FPSC are 1.7, 1.65, and 0.9 mm at the studied tilt angles, respectively.

Techno-economic analysis of a novel retrofit solution for the domestic hot water system: A comparative study

The retrofit solution for domestic hot water (DHW) system in existing buildings requires to ensure the long-term energy security and efficiency as well as to minimise occupants’ disturbance, construction works and installation costs. In this regard, the present study performs a techno-economic evaluation on a novel retrofit solution for DHW production in a pilot building. The proposed solution appoints a substantial role to the thermal energy storage through a 2-pipe hot water network utilisable for both DHW and heating purposes. The first storage level is provided by a centralised buffer storage supplied by a PV-BESS-driven heat pump while the second level consists of decentralised modular tanks installed in each dwelling for the production and storage of hot water. Firstly, experimental thermal performance of the proposed decentralised storages is investigated. By developing a dynamic simulation code, the energy efficiency of the proposed solution is compared to that of the existing system in the pilot building as well to that of a typical centralised system as a benchmark solution. Finally, economic analysis of the retrofit solution is performed to address capital expenditures of the system, including purchasing and installation costs, as well as its life cycle cost (LCC). The obtained results indicate that the proposed system reduces the annual energy consumption for DHW production more than 7,200 kWh, with respect to the existing DHW system. Furthermore, it is shown that, in the proposed system, the fraction of thermal loss from piping network decreases by 31.5%, compared to a typical DHW centralised system. Economic assessment of the proposed solution implies that this system, in terms of both mechanical and electrical components, requires 13.7% lower initial investment than a typical centralised system. However, the cost of control systems in this system is higher since it is inherently a control-based system.

Performance evaluation of an enhanced self-storing evacuated tube solar collector in residential water heating application

Phase change materials (PCMs) offer higher levels energy storage density than conventional hot water tanks commonly used with solar hot water systems. The present study aims at investigating the integration of a selected PCM within the structure of an evacuated tube solar hot water system to create some compact thermal storage capacity. Then conventional solar water heater is compared with this novel PCM-based self-storing design. The results show that the proposed self-storing design can maintain the collector output temperature at around 63 °C after 15 h of not receiving any sunlight. That is whilst the output temperature of the normal collector drops down to ambient temperature in the same period. The obtained energy storage efficiency is 57 % and 75 %, and overall thermal efficiency is 49 % and 72 %, for the normal and the self-storing collectors, respectively. For the small-scale system used in this study, the proposed design helps reduce the size of the hot water storage tank required to supply the hot water demand by 55 %. The study also shows that the same design can even yield better performance at larger scales used in practical applications.

Optimal design modeling of an energy system for a near-zero energy restaurant with green hydrogen energy storage systems

In this research, we want to analyze the consumed energy of an nZEB restaurant in a typical city to anticipate tourists. The energy of this restaurant is supplied through solar panels and electricity grids and we use the hydrogen storage tool because of its advantages to store energy. In this regard, Using the Fanger model, the thermal comfort of passengers was assessed, the energy consumption rate was obtained for the refrigerator, HVAC, lights, and systems, and the consumed water of the restaurant is supplied. Trnsys software was used for this simulation, and the transient performance of the mentioned nZEB in a year is evaluated by Trnsys software. PV panels are used to supply the consumed electricity of the building, A tank stores hydrogen and the extra produced electricity that can be used as needed if sunlight is scarce or electricity is needed. A solar collector is used to generate hot water, and a water tank is used to store the generated hot water. A heat pump is used to supply the cooling load and heating. The consumed hot water by the dwellers is supplied using the stored hot water. With the help of MATLAB software, the Fanger model is used to evaluate the thermal comfort of dwellers. The energy and performance of the restaurant refrigerator are obtained by TRNSYS and EES software. The results show that a significant part of the restaurant's electricity is supplied using 140 PV panels with 0.89 area. In addition, the initial hydrogen pressure tank was lower than the final hydrogen pressure tank. In this regard, energy for the heat pump, refrigerator, light, pump, fan, and compressors is supplied well. Using 16 square meters of solar collectors, the building gets its hot water. Furthermore, the restaurant's air conditioning system provides thermal comfort throughout the year. As a result, using the building roof area for ZEB can significantly reduce the greenhouse gas emissions of Doha.

Energy, exergy, economic and environmental (4E) analysis using a renewable multi-generation system in a near-zero energy building with hot water and hydrogen storage systems

Energy, exergy, economic and environmental (4E) analysis using a renewable multi-generation system in a near-zero energy building with hot water and hydrogen storage systems

5E analysis of a novel designed hot water storage header integrated vacuum tube solar water heater

In this study, 5-E analysis of a heat pipe equipped vacuum tube collector system for residential warm water application has been carried out. The issue of overheating in heat pipes and low thermal efficiency is the major key issues associated with heat pipe vacuum tube collector. This design completely removes the problem of overheating. In addition to this copper fins mounting with condensers of heat pipe enhance the heat transmission rate between the condenser & water stored in a manifold. The results of an experimental investigation reveal that thermal and exergy outputs of the proposed system were obtained almost 63–74% and 4–10% respectively. The average energy gain at the end of the days selected for Run-A, B, and C was calculated to be 7505, 6912, and 6619 kJ respectively, whereas the average exergy gain for corresponding runs was found to be 928, 700, and 401 kJ respectively. In addition to this, the proposed system can provide hot water of approximately 125 L, 76 L, and 52 L in temperatures 50 °C, 55 °C, and 60 °C respectively.Concerning to techno-economic investigation, the per liter cost of warm water generation for the proposed & electric geyser was observed to be 0.15 INR/L & 0.47 INR/L respectively. The levelized energy cost, net present worth, and payback time were found to be 5.48 INR/kWh, 55,819 INR, and 4.12 years respectively. The amount of CO2 mitigation by the developed system was found to be 18.76, 17.28, and 16.54 tCO2/lifetime for Run-A, B & C respectively.

Effect of initial temperature of water in a solar hot water storage tank on the thermal stratification under the discharging mode

Thermal stratification in a storage tank is an important factor affecting hot water output. There are many factors affecting thermal stratification, and the initial temperature in the tank is a notable one. In this paper, a typical solar hot water storage (HWS) tank, which is widely used in practical applications, has been selected to study numerically the effect of the initial temperature on the thermal stratification under the discharging mode. The flow mechanism, temperature distribution, thermal stratification, and thermal mixing mechanism in the tank are analyzed with the numerically simulated results for five initial temperatures in the tank. In addition to the qualitative observation, a quantitative analysis of the effect of the initial temperature in the tank has also been conducted in terms of several key dimensionless parameters which quantify the extent of the thermal stratification in the tank. The results show that the dimensionless exergy decreases with the dimensionless time. When the dimensionless time increases from 0.1 to 0.8, the dimensionless exergy decreases by nearly 0.4. Additionally, a higher initial temperature leads to a smaller extent of the initial mixing and a larger output rate of hot water. When the initial temperature in the tank increases from 313 K to 353 K, the output rate of hot water increases by nearly 11%. Moreover, the extent of the thermal stratification increases almost linearly with the initial temperature in the tank. When the initial temperature in the tank increases from 313 K to 353 K, a 17% increase in the thermal stratification has been achieved indicating that the initial temperature in the tank has a significant effect on the thermal stratification, which will be insightful for the better design of solar hot water systems.

Weather influence on the performance of solar collector

A laboratory-scale evacuated tube solar collector (ETSCs) has been developed and tested for unloading conditions in Lanzhou, China. clear sky and cloudy conditions have been tested. Heat is generally considered instantaneous because it is a function of multiple instantaneous factors, like ambient temperature and solar radiation. The results show a clear sky day with a maximum and average value of ambient temperature, outlet, inlet, and solar radiation of 12 and -60C, 56 and 310C, 69 and 340C, 931 and 576W/m2, respectively, while a cloudy day was eight and -30C and 861.2 and 449W/m2 respectively. Clear sky day maximum and the average mass flow rate was 0.25 and 0.21 Kg/sec, while the cloudy flow rate was 0.27 and 0.03 Kg/sec, respectively. A clear sky has a heat loss of -0.307 and -0.05kW for a cloudy day. R square were 0.76 and 0.4 for clear sky and cloudy day, respectively. For the heat and radiation correlation relationship, a clear sky has a slope of 0.0029 and 0.0539 for a cloudy day. In other conditions, the solar radiation per unit area increases by 1 W/m2, and the daily heat is collected. Increasing A W/m2, the temperature difference between the average temperature of the hot water storage tank and the average temperature of the environment increases by one °C, and the daily heat collection decreases A W/m2. It concludes that a clear sky has much better efficiency than a cloudy day.

Energy and stress analysis of a hybrid photovoltaic thermal module

Photovoltaic (PV) solar panel systems are widely used for meeting domestic electricity requirements because of their simple and cost-effective operation. It is well known that the electrical efficiency of PV panels is abruptly disturbed by cell temperature which depends upon several factors, including ambient temperature. In this study, the increased electrical efficiency of a PV module has been demonstrated by integrating a water storage tank at the backside of the PV module turning the simple PV module into hybrid Photovoltaic Thermal (PVT) module. The water tank acts as the reservoir and provides water flow at the backside of the PV module and the temperature difference between water and cell causes the heat exchange between the back surface of the PV panel and water, resulting in the lowering of the PV module cell temperature. This hybrid design has resulted in a 19% increment in the electrical efficiency of the PV panel. The system is designed to store hot water at 40 °C. In addition, a PVT thermal efficiency of 36.5% is also achieved which can be used to meet hot water domestic applications. The structural analysis of the system design through ANSYS® is also carried out to determine the effects of water pressure on the tank and it has been found that the design is safe and secure.

Model predictive control of solar-coupled innovative heat pump: a comparison of economic and environmental optimizationsin Latvia.

Background: Heating and cooling in buildings represents a significant amount of the energy demand in the EU, but the market penetration of renewable solutions is still marginal. The SunHorizon project aims at proving the viability and benefits of innovative coupling between heat pumps and various advanced solar panels. Methods: This study focuses on the optimal operation strategies of a technological package located in Latvia, and composed of hybrid photovoltaic thermal (PVT) panels, a gas driven heat pump and a hot water storage tank. In this work, a model predictive control is developed, based on mixed integer linear programming (MILP) optimization. This model uses innovative elements compared to traditional model predictive control (MPC), with environmental indicators for the Latvian electricity grid accounting for imports, co-simulation with TRNSYS using the transmission control protocol (TCP) and modelling of long-term storage for long and short-term decisions. The usual minimization of costs is compared to two new optimization approaches, which aims to minimize greenhouse gas (GHG) emissions and maximizing renewable use and self-consumption. Results and conclusions: The results of the optimization of costs and GHG emissions show that gains can be found within the variations in time series related to the electricity grid, but the overall operation strategies remain similar. Optimization of renewable share and self-consumption is another path for control strategy, but with less economic and environmental performance.

Energy use and energy efficiency in cruise ship hotel systems in a Nordic climate

In light of climate change, the shipping industry is committed to reducing its greenhouse gas emissions. When transitioning from fossil fuels to low-carbon fuels, it is crucial to also reduce the ships' energy need. For cruise ships, the hotel system is a major energy consumer and the focus of this paper. This study aims to investigate the energy use of an existing fossil-fuelled cruise ship operating in a Nordic climate, and evaluate the effectiveness of various passive and active energy-saving measures. For this purpose, a dynamic energy model of the hotel system was developed in the building simulation tool IDA Indoor Climate and Energy (IDA ICE), including a customised weather file. Validation of the model was achieved through comparison with literature and some operational data from the actual cruise ship. Simulation results showed a total annual energy use of 55 MWh/passenger, with the hotel system accounting for 20%. The passive measures, such as increased insulation and improved windows, each resulted in less than a 1% reduction in the hotel's annual energy use. Larger energy savings were achieved by using heat pumps (38%), improved ventilation system (8–24%), and heating setback in port and during the night (5%). A hot water storage tank, charged with the engines' waste heat during sea operation, could reduce the use of auxiliary boilers, especially in port. A hot water tank of 600 m3 could cover 97% of the heating demand in port, thereby minimising the use of fuel-fired boilers.

Modeling and Simulation of Indirect Collector Solar Hot Water Heating System Based on TRNSYS

The use of solar energy is one of the important ways of clean energy heating in rural areas in the north, and the collector solar water heating system is an effective way to use solar energy. This paper takes a typical single residential house in a rural area of Shenyang as a research case to design an indirect collector solar hot water heating system. Based on the meteorological data of the winter heating period (November 1 - March 31 of the following year) in Shenyang, TRNSYS software was used to research the heat collection efficiency and scheme design of the heating system. The research results showed that: 1) The best material of the heat exchange coil of the hot water storage tank in the solar water heating system of the indirect collector is stainless steel with a thickness of 0.8mm; 2) The optimal installation angle of solar collectors in Shenyang is 55°; 3) The optimal area of the heat exchanger coil in the hot water storage tank is 4.40m2.

Energy analysis of a small-scale multi-effect distillation system powered by photovoltaic and thermal collectors

Powering thermal desalination technologies by renewable energy is believed to be a viable solution to overcome the worldwide freshwater scarcity problem without causing more damage to the environment. In this paper, a multi-effect distillation system (MED) with mechanical vapor compression is powered by the generated electrical power of photovoltaic/thermal collectors and assisted by the by-product thermal power generated. The system is sized according to thermal power needed and designed for small-scale application and weather conditions of Alexandria, Egypt. Excess electricity is injected into the grid and hot water storage tank is used as a back-up to compensate low and fluctuating radiation. Results show that, at a saturation temperature of MED’s heating steam of 55 °C, freshwater production is 11.1 m3/day in 10 hours of operation, system specific power consumption is 9.72 kWh/m3, specific area is 317.04 m2s/kg, and performance ratios of the desalination unit is 3.33 and 6.97 for the overall system. However, at T = 65 °C the system’s electrical energy is totally absorbed by the compressor, and the system’s performance decreases.

Large heat pumps with hot water store in local heating systems – Investigation of operation strategies

In the context of the German energy transition, heat pump technology utilizing heat and electricity from renewable sources is an alternative to traditional fossil fuel based boilers, which enables a sustainable heat supply. Therefore, the transformation of a residential area in Germany into a zero-emissions district employing a heat-pump-based local heating system with hot water store is investigated. The heat pumps are supposed to use the return flow of an existing district heating network as heat source. Most commercially available heat pumps have a standard temperature spread from 3 K to 5 K in the evaporator. In this case, the given limited source flow rate leads to a relatively low heat capacity of the heat pumps (output), which requires an unusual large dimension of the hot water store and impairs the economic efficiency of the heating system. To ensure an optimal store dimension, a possible solution is to install a mixing circuit on the heat source side of the heat pump (with a 5 K temperature spread in the evaporator) to increase the temperature spread of the heat source by remixing the return water, whereby the coefficient of performance for heating becomes smaller. Another solution is to raise the temperature spread in the evaporator directly (design of heat exchanger), also in this case, the coefficient of performance for heating diminishes. Here, we present the theoretical investigation of two heat pump configurations as well as operating strategies: a) Installation of a mixing system in the heat pumps with standard temperature spread in the evaporator (5 K) and b) constant water flow through the evaporator with varying temperature spread up to 15 K. The heat pumps were simulated using the program EBSILON®Professional. The simulations show that the strategy a) achieves higher coefficient of performance εh, HP within low heating capacity range (300 kW to 750 kW), while the strategy b) has better coefficient of performance εh, HP within high heating capacity range as well as a larger total heating capacity range up to 1750 kW. The result is a better annual coefficient of performance for heating of the strategy b) in the system simulations (heat pumps and hot water store system operation) using the Program TRNSYS. The hot water store decouples heat pump operation from heat load to ensure that the heat pumps always work at the optimum operating points.

Calculation of Volume of Hot Water Storage Tank in Air Source Heat Pump System

Air source heat pump integrated with hot water storage tank may enhance the efficiency of heating, and the volume of hot water storage tank is closely related to the thermal efficiency of the hot water system. Referring to the relevant formulas of building water supply and drainage design standards, this paper simulates the operation conditions of heat pump, and combined with the measured annual data of hot water using in a hospital, systematically discusses the adaptability of heat pump water production and seasonal hot water usage, as well as the actual regulating volume of hot water storage tank. Assumed the heat pump is altered by the working condition of the vernal equinox, the daily storage and discharge of the hot water tank can be accurately calculated, the hot water tank should charge 2.94 times of average hourly water yield of air pump during the peak water usage period. considering the safety and economy of the air source heat pump system, it is strongly recommended that the volume of hot water storage tank can be designed as the 5 ~ 6 times of hourly average water yield of air source heat pump, which can meet the usage of hot water for most of the time and it is inspected under various accidental conditions.

Modeling and control method of combined heat and power plant with integrated hot water storage tank

To enhance the flexibility of conventional power plants, a dynamic mathematical model of a combined heat and power unit is developed and verified in this study using field data, and the maximum relative error is less than 5%. Subsequently, the dynamic characteristics of the coal-fired power plant with the hot water storage tank are studied, and the temperature distribution curve inside the hot water storage tank is obtained. Finally, a new coordinated control system with an integrated hot water storage tank is designed. The new coordinated control system reduces the fluctuation in the heating load caused by the unit in the process of changing the load. The integral of absolute value of the error criterion and integral of time multiplied by the squared error criterion results for unit loads at different variable load rates are at least 200 and 50,000 lower compared to conventional control methods. This study provides a new solution to the problem that the current conventional turbine and boiler coordinated control system cannot address the difficulty of renewable energy power consumption, which is important for the safe and stable power grid operation after the large-scale grid connection of renewable energy power.

Experimental Performance and Cost-Effectiveness of a Combined Heating System under Saharan Climate

The solar water heater can be integrated into future residential buildings as the main energy source, which will subsequently reduce the energy cost of water heating. An original configuration for an efficient Domestic Hot Water (DHW) storage tank is developed and experimentally evaluated under Saharan climate. This novel DHW configuration includes a hybrid (solar and electric) energy system with a flat plate solar collector coupled with an electric heater. Additionally, a phase change material (PCM) mixture that is composed of paraffin wax and animal fat with a melting temperature between 35.58 °C and 62.58 °C and latent heat between 180 and 210 kJ/kg is integrated into this novel tank configuration. The experimental results indicated that hot water production by using latent heat storage could be economically attractive. By evaluating the cost of water heating expressed in Algerian dinar per liter (DZD/L), it was found that one liter of hot water may cost around 0.1362 DZD/L (i.e., 0.00096 USD/L) compared to 0.4431 DZD/L for the conventional water heater, an average energy cost savings of 69.26%. On a yearly basis, the average energy cost savings may reach up to 80.25% if optimal tilt for the solar collector is adopted on a monthly basis. The flat plate collector may be vulnerable to convective heat transfer; therefore, other solar collectors, such as vacuum tube collectors, may provide enhanced energy performance.

Thermal and chemical reliability of paraffin wax and its impact on thermal performance and economic analysis of solar water heater

In the current investigation, two hot water storage tank integrated evacuated tube collector systems have been designed and fabricated. In one of the systems, an evacuated tube integrated with PCM (phase change material) is termed a testing system while another evacuated tube system was left without PCM termed a reference system. Based on the experimental results, it has been found that the incorporation of paraffin wax in the testing system improved the thermal energy output. Also, the thermal cycling of selected PCM has undergone up to 1500 cycles and results showed very negligible changes in its chemical and thermal properties. The useful energy output of the system with PCM has been improved by 36.81 %, 26.97 %, and 22.72 % for Run_40oC, Run_45oC, and Run_50oC respectively. In addition to this, extra hot water obtained from the testing system was 14 L for Run_40oC, 5 L for Run_45oC, and 6 L for Run_50oC respectively as compared to the reference system. Concerning techno-economic analysis, on average, the value of per litre cost of production of hot water (CPL) by the proposed system and electric water heater was observed to be INR 0.16 and INR 0.48 respectively. The net present value of the proposed system was found to be approximately INR 11598 and total expenditure on the proposed system can be recovered after 4.07 years which is much shorter compared to the life of the proposed system.The present work removes the overheating issue of heat pipes and improves the performance of the system by modifying in design and utilization of paraffin wax as heat storage material.

Model predictive control of sun-coupled innovative heat pumps: a comparison of economic and environmental optimizations

Background: Heating and cooling in buildings represents a significant amount of the energy demand in the EU, but the market penetration of renewable solutions is still marginal. The SunHorizon project aims at proving the viability and benefits of innovative coupling between heat pumps and various advanced solar panels. Methods: This study focuses on the optimal operation strategies of a technological package composed of hybrid photovoltaic thermal (PVT) panels, a gas driven heat pump and a hot water storage tank. In this work, a model predictive control is developed, based on mixed integer linear programming (MILP) optimization. This model uses innovative elements compared to traditional model predictive control (MPC), with environmental indicators for the electricity grid accounting for imports, co-simulation with TRNSYS using the transmission control protocol (TCP) and modelling of inter-seasonal storage for long and short-term decisions. The usual minimization of costs is compared to two new optimization approaches, which aims to minimize greenhouse gas (GHG) emissions and maximizing renewable use. Results and conclusions: The results of the optimization of costs and GHG emissions show that gains can be found within the variations in time series related to the electricity grid, but the overall operation strategies remain similar. Optimization of renewable share and self-consumption is another path for control strategy, but with less economic and environmental performance.